1. Field of the Invention
The present invention relates to a test of a semiconductor device utilizing electron beam. Particularly, the present invention relates to a device test in which the quality of a sample to be tested is determined by measuring electric current flowing through the test sample when the latter is irradiated with electron beam.
2. Description of the Related Art
There has been a semiconductor device tester for testing contact holes or through-holes of a semiconductor device by utilizing electron beam. For example, JP H10-281746A discloses a semiconductor device tester in which a contact hole is irradiated with electron beam and the contact hole is decided as opened when a current flows through the device and decided as not opened when no current flows. In this semiconductor device tester, a diameter of a bottom of the contact hole can be measured by a time difference of current measured correspondingly to electron beam scan time.
With the popularization of SOC (System-On-Chip) semiconductor devices, logic circuits such as memories and CPU, etc., have been formed in a semiconductor device. Since, in general, there is no regularity of layout of a logic circuit, positions of contact holes are generally arranged at random. The above mentioned technique can be utilized in order to test the contact holes arranged at random.
However, in order to reflect the measured current to the quality of the contact hole, it is necessary to know a portion of the measured current corresponding to the contact hole. Therefore, it is necessary to obtain an information of positions of all of contact holes by using CAD data and to prepare the data for every semiconductor device.
On the other hand, with the recent accelerated popularization of semiconductor device integration, semiconductor devices exceeding 10 billions in number can be integrated on one chip. In such case, a memory capacity necessary to memorize a layout of each of layers of the chip becomes several G bytes. It is practically impossible to prepare a tester for one device and there are many kinds of logistic device produced in a mass production factory. Therefore, in order to specify positions of through-holes by using CAD data, it is necessary to accumulate a massive amount of data and it is difficult to accumulate all of the data in a single tester.
An object of the present invention is to provide a test method of a semiconductor device and a semiconductor device tester with which a correct result of test can be obtained without using CAD data even where through-holes are randomly arranged like a logic circuit.
According to a first aspect of the present invention, a semiconductor device tester including electron beam irradiation means for irradiating a sample to be tested (referred to as xe2x80x9ctest samplexe2x80x9d, hereinafter) by scanning a surface of the test sample with electron beam and current measuring means for measuring current generated in the test sample by the irradiation of electron beam is featured by comprising memory means for storing a variation of current value of each of a plurality of test samples which is measured by the current measuring means while moving an irradiating position of electron beam by the electron beam irradiation means as a current waveform corresponding to the electron beam irradiating position, and comparison means for comparing the current waveforms obtained from the plurality of the test samples and stored in the memory means and outputting an information related to positions on the test samples when there is a difference in current value between the stored current waveforms, which exceeds a predetermined value.
Practically, the memory means functions to store the current waveforms obtained in the two test samples formed on one wafer and the comparison means preferably compares the current waveforms of the test samples with each other. However, it is not always necessary to use two test samples formed on the same wafer. On demand, one of the current waveforms to be obtained from two test samples may be preliminarily obtained from one of the two test samples.
It is preferable that the electron beam irradiation means can set a beam width of electron beam to a value substantially equal to a diameter of a contact hole formed in a test sample and, after the test sample is scanned with the electron beam in a scan line direction, can shift the scan line in a direction perpendicular to the scan line direction by a distance corresponding to the width of the electron beam. Further, it is more preferable that the electron beam irradiation means can set a beam width of electron beam to a value smaller than a diameter of a contact hole formed in a test sample and, after the test sample is scanned with the electron beam in a scan line direction, can shift the scan line in a direction perpendicular to the scan direction by a distance substantially equal to the diameter of the contact hole. Further, it is preferable that the electron beam irradiation means can set a width of electron beam such that a plurality of contact holes formed in a test sample are irradiated with the electron beam simultaneously and, after the test sample is scanned with the electron beam in a scan line direction, can shift the scan line in a direction perpendicular to the scan line direction by a distance substantially equal to the beam width. Further, it is preferable that the electron beam irradiation means can set a width of electron beam such that an area of a test sample, which includes a plurality of contact holes, is irradiated with the electron beam simultaneously and, after the test sample is scanned with the electron beam in one scan line direction, can shift the scan line in a direction perpendicular to the scan line direction by a distance substantially equal to the beam width. The electron beam irradiation means may comprise main scan means for scanning a test sample with electron beam by shifting the test sample and sub scan means for deflecting the electron beam in a direction different from the main scan direction while the main scan means is scanning the test sample.
In a case where electron beam having width smaller than the diameter of the contact hole is used, the comparison means may comprise means for comparing instantaneous current values of a plurality of test samples each measured at an intermediate position between a rising edge and a falling edge of a current waveform generated in a certain circuit pattern. Alternatively, in a case where the electron beam having width substantially equal to or smaller than the diameter of the contact hole is used, the comparison means may comprise means for integrating current flowing from a rising edge to a falling edge of a current waveform generated in a certain circuit pattern, divider means for dividing a result of integration from the integrating means by a distance between the rising edge and the falling edge of the current waveform and average value comparison means for comparing average current values obtained by the divider means. The comparison means may comprise integration value comparing means for integrating current values of current waveforms measured at same circuit pattern positions and comparing the integrated current values.
Further, the semiconductor device tester according to the present invention may comprise means for frequency-analyzing measured current waveforms while moving an irradiating position of electron beam and means for grouping positions of the test sample, at which the current waveforms are acquired, every area having same frequency component according to the frequency analysis. In such case, the semiconductor device tester preferably comprises means for setting a test method correspondingly to frequency component of each of grouped areas.
The comparison means may comprise means for calculating an intermediate position between a rising position and a falling position of a pulse contained in a current waveform as a center position of a contact hole and means for comparing relative positions of the center positions of contact holes calculated for two test samples.
According to a second aspect of the present invention, a test method using the above described semiconductor device tester is featured by comprising the steps of irradiating a first test sample, which is formed in a circuit pattern, with electron beam, which has a rectangular cross section and width substantially equal to a diameter of a contact hole, while scanning the electron beam in a direction perpendicular to a longitudinal direction of the rectangular cross section of the electron beam, shifting a scan position in a direction perpendicular to the scan direction by a distance corresponding to the diameter of the contact hole every time when one line scan is completed, storing a current value generated in the first test sample when the latter is irradiated with electron beam as a first current waveform by corresponding the current value to position irradiated with electron beam, irradiating a second test sample, which is formed in the same circuit pattern, with electron beam, which has a rectangular cross section and width substantially equal to a diameter of a contact hole, while scanning the electron beam in a direction perpendicular to a longer side direction of the rectangular cross section of the electron beam, shifting a scan position by a distance corresponding to the diameter of the contact hole in a direction perpendicular to the scan direction every time when one line scan is completed, storing a current value generated in the second test sample when the latter is irradiated with electron beam as a second current waveform by corresponding the current value to position irradiated with electron beam, comparing the first current waveform with the second current waveform and extracting coordinates of a position at which a difference in current value between the first and second current waveforms becomes equal to or larger than a predetermined value.
According to a third aspect of the present invention, a test method using the above described semiconductor device tester is featured by comprising the steps of irradiating a first test sample, which is formed in a circuit pattern, with electron beam having width smaller than a diameter of a contact hole while scanning the electron beam in one direction, shifting a scan position in a direction perpendicular to the scan direction by a distance corresponding to the diameter of the contact hole every time when one line scan is completed, storing a current value generated in the first test sample when the latter is irradiated with electron beam as a first current waveform by corresponding the current value to position irradiated with electron beam, irradiating a second test sample, which is formed in the same circuit pattern, with electron beam having width smaller than a diameter of the contact hole while scanning the electron beam in one direction, shifting a scan position by a distance corresponding to the diameter of the contact hole in a direction perpendicular to the scan direction every time when one line scan is completed, storing a current value generated in the second test sample when the latter is irradiated with electron beam as a second current waveform by corresponding the current value to position irradiated with electron beam, extracting instantaneous current values of the first and second current waveforms each measured at an intermediate position between a rising position and a falling position of each of the first and second current waveforms corresponding to the same circuit pattern, comparing the instantaneous current values with each other and extracting coordinates of a position at which a difference in current value between the first and second current waveforms becomes equal to or larger than a predetermined value.
According to a fourth aspect to the present invention, a test method using the above described semiconductor device tester is featured by comprising the steps of simultaneously irradiating a plurality of contact holes of a first test sample, which are formed in a circuit pattern, with electron beam having a rectangular cross section, while scanning the first test sample with the electron beam in a direction perpendicular to a longer side direction of the rectangular cross section of the electron beam, shifting a scan position in a direction perpendicular to the scan direction by a distance corresponding to a width of the electron beam every time when one line scan is completed, storing a current value generated in the first test sample when the latter is irradiated with electron beam as a first current waveform by corresponding the current value to position irradiated with electron beam, simultaneously irradiating a plurality of contact holes of a second test sample, which are formed in the same circuit pattern, with electron beam having a rectangular cross section, while scanning the second test sample with the electron beam in a direction perpendicular to the longer side direction of the rectangular cross section of the electron beam, shifting a scan position by a distance corresponding to the width of the electron beam in a direction perpendicular to the scan direction every time when one line scan is completed, storing a current value generated in the second test sample when the latter is irradiated with electron beam as a second current waveform by corresponding the current value to position irradiated with electron beam, comparing the first current waveform with the second current waveform and extracting coordinates of a position at which a difference in current value between the first and second current waveforms becomes equal to or larger than a predetermined value.
According to a fifth aspect of the present invention, a test method using the above described semiconductor device tester is featured by comprising the steps of scanning a first test sample with electron beam by simultaneously irradiating an area of the first test sample containing a plurality of contact holes, which are formed in a circuit pattern, with the electron beam, shifting a scan position by a distance corresponding to a diameter of the contact hole in a direction perpendicular to the scan direction every time when one line scan is completed, storing a current value generated in the first test sample when the latter is irradiated with electron beam as a first current waveform by corresponding the current value to position irradiated with electron beam, scanning a second test sample with electron beam by simultaneously irradiating an area of the second test sample, which contains a plurality of contact holes formed in the same circuit pattern, with electron beam, shifting a scan position by a distance corresponding to a diameter of the contact hole in a direction perpendicular to the scan direction every time when one line scan is completed, storing a current value generated in the second test sample when the latter is irradiated with electron beam as a second current waveform by corresponding the current value to position irradiated with electron beam, integrating the first and second current waveforms and comparing the integrated current waveforms and extracting coordinates of a position at which a difference in current value between the first and second current waveforms becomes equal to or larger than a predetermined value.
According to a sixth aspect of the present invention, a test method using the above described semiconductor device tester is featured by comprising the steps of storing a current value generated in a test sample when the test sample is scanned by irradiating the latter with electron beam as a current waveform by corresponding the current value to position irradiated with electron beam, integrating current flowing from a rising edge to a falling edge contained in the current waveform, dividing a result of the integration by a distance between the rising edge and the falling edge of the current waveform, comparing a result of the division with a preliminarily stored reference value and determining the quality of the test sample on the basis of a result of the comparison.
According to a seventh aspect of the present invention, a test method using the above described semiconductor device tester is featured by comprising the steps of scanning a first test sample by irradiating the first test sample, which is formed in a circuit pattern, with electron beam, storing a current value generated in the first test sample when the latter is irradiated with electron beam as a first current waveform by corresponding the current value to position irradiated with electron beam, integrating a current flowing from a rising edge to a falling edge contained in the current waveform, obtaining a first mean value by dividing a result of the integration by a distance between the rising edge and the falling edge of the current waveform, scanning a second test sample by irradiating the second sample, which is formed in the circuit pattern, with the electron beam, storing a current value generated in the second test sample when the latter is irradiated with electron beam as a second current waveform by corresponding the current value to position irradiated with electron beam, integrating a current flowing from a rising edge to a falling edge contained in the current waveform, obtaining a second mean value by dividing a result of the integration by a distance between the rising edge and the falling edge of the current waveform and determining the quality of the first and second samples by comparing the first mean value with the second mean value.
In the test method mentioned above, it is possible to alternately perform a sub scan of a constant amount in a second direction different from a first direction along which a main scan of electron beam is performed or a third direction opposite to the second direction, every time when the main scan of electron beam proceeds in the first direction by a distance corresponding to a diameter of a contact hole contained in a test sample.
It is possible to group positions, at which current waveforms are acquired, every area having same frequency component by frequency-analyzing at least one of the current waveforms. In such case, it is possible to set one of the test methods to every grouped area correspondingly to the frequency component thereof.
According to an eighth aspect of the present invention, a test method using the above mentioned semiconductor device tester is featured by comprising the steps of scanning a first test sample, which is formed in a circuit pattern, by irradiating the first test sample with electron beam, storing a current value generated in the first test sample as a first current waveform by corresponding the current to positions of the test sample irradiated with the electron beam, calculating an intermediate position between a rising edge and a falling edge of the first current waveform as a center position of a contact hole, scanning a second test sample, which is formed in the circuit pattern, by irradiating the second test sample with electron beam, storing a current value generated in the second test sample as a second current waveform by corresponding the current to positions of the second test sample irradiated with the electron beam, calculating an intermediate position between a rising edge and a falling edge of the second current waveform as a center position of a contact hole, comparing the center position obtained for the first test sample with the center position obtained for the second test sample and, when a difference in current value between the centers becomes equal to or larger than a predetermined value, extracting coordinates of the corresponding center position.